Is my Betta dying? Please help!

My Betta has been laying at the bottom of his tank since yesterday morning. I transferred him to his new tank the night before. I have him in a 10 gallon tank with a filter (current slowed down by water bottle in front of it), a heater, a few silk plants, a miss ball, and a little floating plant (both plants titled for Bettas). He will eat fine when I put food in and moved around for the net being put in when I was almost sure he had died. He won't even move when close to the glass when I tap it. His gills are moving slowly and heavily. He is now laying on his side.

Did you make sure the water chemistry in the 10 gal was the same as the water in his old home? (Temperature, ph, Hardness, etc.) Your Betta might be stressed out due to a sudden change in temperature, or something.